The present invention relates to a vehicle air conditioner to be mounted on a vehicle, and more particularly relates to an air conditioner with a heat pump device.
An air conditioner with a heat pump device has been known in the art as an air conditioner to be mounted on electric vehicles and other kinds of vehicles. A heat pump device for use in each of those vehicles is formed by connecting together an electric compressor, an exterior heat exchanger provided outside the vehicle cabin, a pressure reducing valve, and an interior heat exchanger provided inside the vehicle cabin in this order via refrigerant piping (see, for example, Japanese Unexamined Patent Publication No. 2011-5983).
When the heat pump device operates in a heating operation mode, the refrigerant is allowed to flow so that the interior heat exchanger functions as a radiator and the exterior heat exchanger functions as a heat absorber. On the other hand, when the heat pump device operates in a cooling operation mode, the refrigerant is allowed to flow so that the interior heat exchanger functions as a heat absorber and the exterior heat exchanger functions as a radiator.
Meanwhile, a vehicle air conditioner as disclosed in Japanese Unexamined Patent Publication No. 2011-255735, for example, includes an upstream interior heat exchanger provided upstream in the airflow direction and a downstream interior heat exchanger provided downstream in that direction. Its refrigerant piping includes a four-way valve. By turning this four-way valve, a switch is made between multiple operation modes such as a heating operation mode and a cooling operation mode.
As another example, a vehicle air conditioner as disclosed in Japanese Unexamined Patent Publication No. H09-240266 includes, as interior heat exchangers, an upstream interior heat exchanger provided upstream in the airflow direction and a downstream interior heat exchanger provided downstream in that direction. The downstream interior heat exchanger functions as a radiator in both of heating and cooling operation modes, while the upstream interior heat exchanger functions as a heat absorber in both of the heating and cooling operation modes.
A heat pump device obtains a heating heat source from the outside air by making the exterior heat exchanger function as a heat absorber during the heating operation mode. However, in a situation where the outside air temperature has decreased to around −20° C., for example, it is difficult to absorb heat using the exterior heat exchanger, thus causing a significant decline in heating capacity.
To overcome such a problem, a heat source may be secured by using an electric heater such as a PTC heater. In the case of an electric vehicle, however, the use of an electric heater increases the consumption of a traction battery so much as to shorten its distance to empty. Likewise, in various kinds of vehicles other than electric vehicles, there is a demand for cutting down the power dissipation as much as possible.
In view of the foregoing background, it is therefore an object of the present invention to reduce the overall consumption of energy for air conditioning while maintaining comfortableness of air conditioning not only in cooling but also in heating as well.